All publications cited in this application are herein incorporated by reference.
H2O2 is a reactive oxygen species (ROS) commonly used as a general biocide in wastewater treatment and for cleaning of algal bioreactors prior to restarting batch cultures. H2O2 cannot be used to control microbial pests in large-scale algal cultures because the desired cyanobacteria and eukaryotic algae are naturally very sensitive to H2O2, especially cyanobacteria. H2O2 is a small, non-polar molecule soluble in both water and lipids. Applied exogenously, H2O2 is believed to kill cells by diffusing rapidly through biological membranes and generating highly destructive hydroxyl radicals (OH.) through Fenton chemistry. H2O2 is also known to directly inhibit thiol-modulated enzymes that participate in photosynthesis and other cellular metabolism. For example, concentrations of H2O2 as low as 10 μM decreased photosynthetic carbon fixation by 50% in plant chloroplasts. Exogenous H2O2 also inhibits turnover of the D1 protein at the translation step of protein synthesis. D1 is part of the core of the Photosystem II (PSII) complex and D1 turnover is necessary for repair of the daily photodamage incurred by PSII. H2O2 is a simple molecule but its effect on cells can be complex. One reason for this is that, in addition to entering freely into cells from exogenous sources, H2O2 is produced endogenously by aerobic metabolism, for example during beta-oxidation of fatty acids or photorespiration. Moreover, H2O2 is a signaling molecule known to activate the SoxR and OxyR regulons and to trigger genes for programmed cell death.
Consistent with its inhibition of metabolism and triggering of cell death, various organisms, including humans and bacteria, utilize H2O2 secretion to defend themselves from pathogens and competitors. A common example is human neutrophils that secrete an “oxidative burst” of lethal H2O2 to kill invading bacteria that they encounter in blood and tissues.
H2O2 is a broad-spectrum biocide effective against unwanted microbes of all kinds. It degrades spontaneously to oxygen (O2) and water (H2O), leaving no residual activity. H2O2 can be applied cheaply at large scales by means of dry compounds that release H2O2 when dissolved in water. Broad-spectrum algaecides with this mode of action are already in use for control of algal blooms in natural waters, e.g. PAK™27.
The foregoing examples of the related art and limitations related therewith are intended to be illustrative and not exclusive. Other limitations of the related art will become apparent to those of skill in the art upon a reading of the specification.